!function(win, lib) {
          var timer,
              doc     = win.document,
              docElem = doc.documentElement,

              vpMeta   = doc.querySelector('meta[name="viewport"]'),
              flexMeta = doc.querySelector('meta[name="flexible"]'),
       
              dpr   = 0,
              scale = 0,
       
              flexible = lib.flexible || (lib.flexible = {});
       
          // 设置了 viewport meta
          if (vpMeta) {
       
              console.warn("将根据已有的meta标签来设置缩放比例");
              var initial = vpMeta.getAttribute("content").match(/initial\-scale=([\d\.]+)/);
       
              if (initial) {
                  scale = parseFloat(initial[1]); // 已设置的 initialScale
                  dpr = parseInt(1 / scale);      // 设备像素比 devicePixelRatio
              }
       
          }
          // 设置了 flexible Meta
          else if (flexMeta) {
              var flexMetaContent = flexMeta.getAttribute("content");
              if (flexMetaContent) {
       
                  var initial = flexMetaContent.match(/initial\-dpr=([\d\.]+)/),
                      maximum = flexMetaContent.match(/maximum\-dpr=([\d\.]+)/);
       
                  if (initial) {
                      dpr = parseFloat(initial[1]);
                      scale = parseFloat((1 / dpr).toFixed(2));
                  }
       
                  if (maximum) {
                      dpr = parseFloat(maximum[1]);
                      scale = parseFloat((1 / dpr).toFixed(2));
                  }
              }
          }
       
          // viewport 或 flexible
          // meta 均未设置
          if (!dpr && !scale) {
              // QST
              // 这里的 第一句有什么用 ?
              // 和 Android 有毛关系 ?
              var u = (win.navigator.appVersion.match(/android/gi), win.navigator.appVersion.match(/iphone/gi)),
                  _dpr = win.devicePixelRatio;
       
              // 所以这里似乎是将所有 Android 设备都设置为 1 了
              dpr = u ? ( (_dpr >= 3 && (!dpr || dpr >= 3))
                              ? 3
                              : (_dpr >= 2 && (!dpr || dpr >= 2))
                                  ? 2
                                  : 1
                        )
                      : 1;
       
              scale = 1 / dpr;
          }
       
          docElem.setAttribute("data-dpr", dpr);
       
          // 插入 viewport meta
          if (!vpMeta) {
              vpMeta = doc.createElement("meta");
               
              vpMeta.setAttribute("name", "viewport");
              vpMeta.setAttribute("content",
                  "initial-scale=" + scale + ", maximum-scale=" + scale + ", minimum-scale=" + scale + ", user-scalable=no");
       
              if (docElem.firstElementChild) {
                  docElem.firstElementChild.appendChild(vpMeta)
              } else {
                  var div = doc.createElement("div");
                  div.appendChild(vpMeta);
                  doc.write(div.innerHTML);
              }
          }
       
          function setFontSize() {
              var winWidth = docElem.getBoundingClientRect().width;
              // console.log(winWidth)
              if ( winWidth > 768 ) {
                docElem.style.fontSize = 16 + "px";
                flexible.rem = win.rem = 16;
                return;
              }
              if (winWidth / dpr > 540) {
                  (winWidth = 540 * dpr);
              }
       
              // 根节点 fontSize 根据宽度决定
              var baseSize = winWidth / 10;
       
              docElem.style.fontSize = baseSize + "px";
              flexible.rem = win.rem = baseSize;
          }
       
          // 调整窗口时重置
          win.addEventListener("resize", function() {
              clearTimeout(timer);
              timer = setTimeout(setFontSize, 300);
          }, false);
       
           
          // 这一段是我自己加的
          // orientationchange 时也需要重算下吧
          win.addEventListener("orientationchange", function() {
              clearTimeout(timer);
              timer = setTimeout(setFontSize, 300);
          }, false);
       
       
          // pageshow
          // keyword: 倒退 缓存相关
          win.addEventListener("pageshow", function(e) {
              if (e.persisted) {
                  clearTimeout(timer);
                  timer = setTimeout(setFontSize, 300);
              }
          }, false);
       
          // 设置基准字体
          if ("complete" === doc.readyState) {
              doc.body.style.fontSize = 12 * dpr + "px";
          } else {
              doc.addEventListener("DOMContentLoaded", function() {
                  doc.body.style.fontSize = 12 * dpr + "px";
              }, false);
          }
        
          setFontSize();
       
          flexible.dpr = win.dpr = dpr;
       
          flexible.refreshRem = setFontSize;
       
          flexible.rem2px = function(d) {
              var c = parseFloat(d) * this.rem;
              if ("string" == typeof d && d.match(/rem$/)) {
                  c += "px";
              }
              return c;
          };
       
          flexible.px2rem = function(d) {
              var c = parseFloat(d) / this.rem;
               
              if ("string" == typeof d && d.match(/px$/)) {
                  c += "rem";
              }
              return c;
          }
      }(window, window.lib || (window.lib = {}));